Thermally Enhanced Self-Trapped Exciton Emission Based on Thermochromic Ag+ doping 0D Zinc-Based Halides

Abstract

Thermochromic materials, known for their unique ability to change optical properties with temperature, have broad applications, including in thermochromic light-emitting diodes (LEDs). However, the scarcity of efficient and stable thermochromic phosphors limits their development. In this study, the development of a novel thermochromic phosphor based on zero-dimensional (0D) inorganic metal halides is reported. The 0D Cs₂ZnBr₄:Ag⁺ phosphors show thermally enhanced self-trapped exciton (STE) emission across a wide temperature range from 120 to 300 K with the emitted wavelength changing correspondingly. Temperature-dependent photoluminescence (PL), time-resolved PL, and density functional theory calculations confirm that the thermally enhanced STE emission originates from the passivated defect/traps in Cs₂ZnBr₄ and the thermally assisted energy transfer from the host to STEs formed by [AgBr₄]^3– tetrahedron with matrix phonons complementing the energy mismatch. Furthermore, the reversible thermochromic LEDs based on Cs₂ZnBr₄:Ag⁺ phosphors are successfully prepared. Overall, these findings provide a future design of high-efficiency thermally enhanced luminescent materials and pave a new way for developing thermochromic materials for functional LED illumination.